The intra-lesional variation of type, level of invasion, and tumour thickness of primary cutaneous malignant melanoma.

In order to evaluate the prognostic importance of type of melanoma, level of invasion and tumour thickness in a retrospective study of cutaneous melanomas, it is prerequisite that the available histological material be representative. To investigate this condition 55 primary cutaneous melanomas were studied randomly by serial block technique. The histological classification of each tissue block as to 1) type of melanoma, 2) level of invasion, and 3) tumour thickness was correlated with the overall classification of the corresponding whole tumour. The typing included 6 groups: Superficial spreading melanoma, lentigo maligna melanoma, nodular melanoma, acral lentiginous melanoma, melanoma of unclassifiable type, and nevoid lesion. The depth of tumour invasion was graded by 5 levels according to Clark et al. The tumour thickness was measured in mm as described by Breslow, and arranged in 6 groups (0--0.75 mm, 0.76--1.50 mm, 1.51-2.25 mm, 2.26--3.00 mm. 3.01--6.00 mm, and more than 6.00 mm). The study revealed a consistently of 95% (52/55) between the type of the central cross section and the type of the whole tumour. In 96% (53/55) of the central cross sections the level of invasion was equal to that of the whole tumour. In 95% (52/55) of the central cross sections the tumour thickness was situated in the same group as that of the whole tumour. It is concluded that type, level and thickness of malignant melanomas can be evaluated in retrospective studies if central cross sections of the melanomas are available for histological examination.